Apparatus and method for feeding back channel quality information and scheduling apparatus and method using the same in a wireless communication system

ABSTRACT

An apparatus and method are provided for feeding back channel quality information and performing scheduling using the fed-back channel quality information in a wireless communication system based on Orthogonal Frequency Division Multiple Access (OFDMA). In the OFDMA wireless communication system, forward performance degradation due to a decrease in an amount of reverse channel quality information is reduced, and also an increase in the reverse load due to channel quality information feedback is suppressed. A base station controls power of a physical channel using information fed back from a mobile station. In a method for feeding back channel quality information from the mobile station, sub-band-by-sub-band channel quality information is measured and channel-by-channel quality information of a number of channels is transmitted in order of sub-bands of better channel quality information. Average channel quality information for a total band is measured and transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of KoreanPatent Application No. 2005-79688 filed Aug. 29, 2005 in the KoreanIntellectual Property Office, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an apparatus and method forfeeding back channel quality information and performing scheduling usingthe fed-back channel quality information in a wireless communicationsystem. More particularly, the present invention relates to an apparatusand method for feeding back channel quality information and performingscheduling using the fed-back channel quality information in a wirelesscommunication system based on Orthogonal Frequency Division MultipleAccess (OFDMA).

2. Description of the Related Art:

Conventionally, a wireless communication system performs communicationthrough a radio channel between mobile stations (MSs) or between an MSand a base station (BS) of a predetermined network. The wirelesscommunication system was initially developed to provide a voice service,but has been advanced to provide a data service in response to userrequests. Technologies are needed which can efficiently transmit datadue to an increase in an amount of data to be transmitted and anincrease in the number of users. According to this need, wirelesscommunication systems transmit user-by-user data by correctly detectingchannel situations between the BS and the MSs.

In a method for detecting the channel situations between the BS and theMSs, each MS measures channel quality of a signal received from the BSand feeds back channel quality information or a channel qualityindicator (CQI). For example, in a typical mobile communication systemusing Orthogonal Frequency Division Multiple Access (OFDMA), each MSmeasures the signal strength of a pilot channel received from the BS andtransmits information about the measured strength to the BS. Then, theBS can detect a channel situation between the BS and an associate MSfrom the reception strength of the pilot channel. Thus, the BSefficiently transmits data by employing the detected channel situationfor scheduling and power control of a forward transmission.

As described above, wireless communication systems are being developedinto systems capable of accommodating an increased number of users andtransmitting a large amount of data. However, the OFDMA mobilecommunication system based on the current voice service has a limitationin transmitting a large amount of data at a high rate. Thus, research isbeing actively conducted on other types of systems rather than the OFDMAsystem.

One system for transmitting a large amount of data at a high rate is awireless communication system based on Orthogonal Frequency DivisionMultiplexing (OFDM). The OFDM is a type of Multi-Carrier Modulation(MCM) scheme for converting a serially input symbol stream, to betransmitted to a user, to parallel form, modulating parallel data in aplurality of orthogonal subcarriers, in other words, a plurality ofsubcarrier channels, and transmitting the subcarrier channels. A schemefor identifying multiple users through the OFDM is OFDMA. A method forconfiguring a channel to transmit one data packet in the OFDMA system isdivided into an Adaptive Modulation & Coding (AMC) transmission schemeand a diversity transmission scheme. The AMC transmission schemeconfigures one physical channel by combining adjacent subcarriers andadjacent symbols, and is referred to as a localized transmission scheme.On the other hand, the diversity transmission scheme configures onephysical channel by combining scattered subcarriers and is referred toas a distributed transmission scheme.

First, a method for allocating orthogonal frequencies to users and atransmission method in the OFDMA mobile communication system will bedescribed with reference to the accompanying drawings.

FIG. 1A illustrates an example of allocating orthogonal frequencyresources to users in the OFDMA mobile communication system, and FIG.11B illustrates another example of allocating orthogonal frequencyresources to users in the OFDMA mobile communication system.

In FIGS. 1A and 1B, the horizontal axis represents time and the verticalaxis represents orthogonal frequencies. As illustrated in FIG. 1A,multiple orthogonal frequency resources can form one subcarrier groupand subcarrier groups are allocated to one communication MS. Further,the subcarrier groups are transmitted during at least one OFDM symboltime. In FIGS. 1A and 1B, reference numeral 101 denotes one subcarrierand reference numeral 102 denotes one OFDM symbol. As illustrated inFIG. 1A, subcarrier groups 103, . . . , 104 are included in areallocation period 105 for reallocating frequency resources.

An example of allocating frequency resources will be described withreference to FIGS. 1A and 1B.

FIG. 1A illustrates an example of transmitting data using AMC technologyin the OFDMA system. As illustrated in FIG. 1A, a total frequency bandis conventionally divided into N subcarrier groups or sub-bands in theOFDM system using AMC and performs AMC operations on a subcarriergroup-by-subcarrier group basis. Hereinafter, one subcarrier group isreferred to as one AMC sub-band. That is, Subcarrier Group 1 denoted byreference numeral 103 is referred to as “AMC Sub-Band 1”, and SubcarrierGroup N denoted by reference numeral 104 is referred to as “AMC Sub-BandN”. In the conventional system, scheduling is performed in a unit ofmultiple OFDM symbols as indicated by reference numeral 105. Asdescribed above, the conventional OFDM system independently performs AMCoperations on multiple AMC sub-bands. Thus, each MS feeds back CQIinformation on a sub-band-by-sub-band basis. The BS receives channelquality information of sub-bands to schedule the sub-bands and transmitsuser data on the sub-band-by-sub-band basis. In an example of thescheduling process, the BS selects MSs of the best channel qualities onthe sub-band-by-sub-band basis and transmits data to the selected MSs,such that system capacity can be maximized.

According to characteristics of the above-described AMC operation, itcan be seen that a good situation is the case where multiple subcarriersfor transmitting data to one MS are adjacent to each other. This isbecause channel response strengths relating to adjacent subcarriers maybe similar to each other but channel response strengths relating to faraway subcarriers may be significantly different from each other whenfrequency selectivity occurs in a frequency domain due to a multipathradio channel. The above-described AMC operation maximizes systemcapacity by selecting subcarriers relating to good channel responses andtransmitting data through the selected subcarriers. Therefore, it ispreferred that a structure can select multiple adjacent subcarriersrelating to good channel responses to transmit data through the selectedadjacent subcarriers. The above-described AMC technology is suitable fora data transmission to a particular user. It is not preferred thatchannels to be transmitted to multiple users, for example, broadcast orcommon control information channels, are adapted to a channel state ofone user.

FIG. 1B illustrates an example of transmitting user data using diversitytechnology in the OFDMA system. As illustrated in FIG. 1B, it can beseen that subcarriers carrying data to be transmitted to one MS arescattered, which is different from the AMC mode of FIG. 1A. Thediversity transmission is suitable for the case where a transmission ofa combination of data of one user in a particular sub-band is not easybecause a data transmitter cannot know a channel state. The diversitytransmission is also suitable for a channel to be transmitted tounspecified users as in broadcasting.

The above-described OFDMA wireless communication system conventionallytransmits packet data. The system for transmitting the packet data hasthe structure of FIG. 2. FIG. 2 is a conceptual diagram illustrating arelation between a BS or Access Point (AP) and MSs or Access Terminals(ATs) in a wireless communication system for performing packet datacommunication.

Referring to FIG. 2, MSs or ATs 211, 212, 213, 214, and 215 communicatewith the BS or AP 200 through a predetermined channel. The BS or AP 200transmits a predetermined reference signal, for example, a pilot signal.The MSs or ATs 211˜215 measure the strength of a signal received fromthe BS 200 and feed back information about the measured strength to theBS or AP 200, respectively. Thus, the BS or AP 200 performs schedulingusing information about strengths of signals received from the MSs orATs and transmits data to the MSs or ATs. In FIG. 2, the arrows from theBS or AP 200 to the MSs or ATs 211˜215 are signals transmitted onforward channels and the arrows from the MSs or ATs 211˜215 to the BS orAP 200 are signals transmitted on reverse channels.

As described with reference to FIG. 2, a mobile communication system forperforming packet data communication widely employs a scheme in which anMS measures the quality of a forward channel and feeds back channelquality information to the BS, because a transmitter of the BS caneasily select a suitable data transmission rate according to a channelstate when knowing a forward channel state.

A scheme for feeding back forward channel quality information from an MSin the OFDMA mobile communication system will be described.

FIG. 3 is a timing diagram illustrating an operation for feeding backforward channel quality information from an MS in the OFDMA mobilecommunication system for performing packet data communication.

Referring to FIG. 3, blocks 301, 302, 303, and 304 indicate that the MSfeeds back forward channel quality information in a block unit. Thechannel quality information is fed back during one feedback informationtransmission. In the OFDMA system, each MS conventionally feeds back apair of a sub-band index and channel quality information. That is, asub-band index and its mapped channel quality information are fed backsuch that sub-band-by-sub-band channel quality information is fed back.Because a large number of sub-bands are conventionally present in theOFDMA wireless communication system, severe reverse load occurs whenchannel quality information of all sub-bands is fed back. Thus, the MSconventionally selects several best sub-bands and feeds back sub-bandindices and their channel quality information.

Because the number of sub-bands capable of being allocated from the BSto the MS is reduced when the number of feedback sub-bands is reduced,the forward performance is degraded. For example, when the MS selectsonly one sub-band and feeds back a sub-band index and its channelquality information to the BS, the BS can allocate only the sub-bandselected by the MS. If the sub-band cannot be allocated to the MS, theforward performance for the MS is degraded.

When the number of feedback sub-bands increases, an increase in thereverse load is caused and therefore the reverse throughput is degraded.In contrast, when the number of feedback sub-bands decreases, theforward channel selectivity is reduced and therefore the forwardperformance is degraded. Thus, a need exists for an improved methodcapable of performing processing such that a relation between thereverse load and the forward channel selectivity is appropriatelyestablished.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention address at least theabove problems and/or disadvantages and provide at least the advantagesdescribed below. Accordingly, an exemplary object of the presentinvention is to provide an apparatus and method that can suppress thereverse load due to feedback while reducing the degradation of forwardperformance due to a decrease in quality information of a reversechannel in an Orthogonal Frequency Division Multiple Access (OFDMA)system.

It is another exemplary object of the present invention to provide anapparatus and method that can efficiently perform scheduling bysuppressing the reverse load due to feedback while reducing thedegradation of forward performance due to a decrease in qualityinformation of a reverse channel in an OFDMA system.

It is yet another exemplary object of the present invention to providean apparatus and method that can control power of a physical channel ofa base station using information fed back from a mobile station.

In accordance with an exemplary aspect of the present invention, thereis provided an apparatus for feeding back channel quality informationfrom a mobile station in a wireless communication system based onOrthogonal Frequency Division Multiple Access (OFDMA), comprising acontroller for measuring sub-band-by-sub-band channel qualityinformation, generating channel-by-channel quality information of anumber of channels in order of sub-bands with better channel qualityinformation, and measuring and generating average channel qualityinformation for a total band in the OFDMA wireless communication system,a modem for encoding and modulating information output from thecontroller and a transmitter for configuring information output from themodem in a physical channel, performing a band up-conversion process forthe physical channel, and transmitting the physical channel.

In accordance with another exemplary aspect of the present invention,there is provided an apparatus for receiving channel quality informationfeedback and performing scheduling in a base station of a wirelesscommunication system based on Orthogonal Frequency Division MultipleAccess (OFDMA), comprising a channel quality information receiver forreceiving, demodulating, and decoding channel quality informationreceived from a mobile station, a controller for extracting averagechannel quality information for a total band and sub-band indexinformation mapped to best channel quality of a particular mobilestation on a basis of information from the channel quality informationreceiver, allocating a channel to each mobile station in adaptivemodulation and demodulation mode using sub-band indices mapped to thebest channel quality and a priority of each mobile station aftercollecting scheduling information, and performing scheduling usingaverage channel quality information of mobile stations for whichallocation is impossible with respect to a sub-band of the best channelquality or only the average channel quality information for the totalband; and a data channel configuration unit for configuring andtransmitting a data channel on a basis of information controlled in thecontroller.

In accordance with another exemplary aspect of the present invention,there is provided a method for feeding back channel quality informationfrom a mobile station in a wireless communication system based onOrthogonal Frequency Division Multiple Access (OFDMA), comprisingmeasuring sub-band-by-sub-band channel quality information andtransmitting channel-by-channel quality information of a number ofchannels in order of sub-bands with better channel quality informationand measuring and transmitting average channel quality information for atotal band in the OFDMA wireless communication system.

In accordance with yet another exemplary aspect of the presentinvention, there is provided a scheduling method for use in a basestation of a wireless communication system based on Orthogonal FrequencyDivision Multiple Access (OFDMA) for measuring and feeding back channelquality information of sub-bands with better channel quality informationand average channel quality information for a total band, comprisingdetermining whether an associated sub-band can be allocated to anassociated mobile station when channel quality information for sub-bandsis comprised, setting a data transmission in adaptive modulation anddemodulation mode and setting a data transmission rate according to thechannel quality information, when the associated sub-band can beallocated and setting a data transmission in diversity mode and settinga data transmission rate according to average channel qualityinformation for a total band, when the associated sub-band cannot beallocated.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A illustrates an example of allocating orthogonal frequencyresources to users in a mobile communication system based on OrthogonalFrequency Division Multiple Access (OFDMA);

FIG. 1B illustrates another example of allocating orthogonal frequencyresources to users in the mobile communication system based on OFDMA;

FIG. 2 is a conceptual diagram illustrating a relation between a basestation (BS) and mobile stations (MSs) in a wireless communicationsystem for performing packet data communication;

FIG. 3 is a timing diagram illustrating an operation for feeding backforward channel quality information from an MS in the OFDMA mobilecommunication system for performing packet data communication;

FIG. 4 is a timing diagram at the time of feeding back forward channelquality information from an MS in accordance with an exemplaryembodiment of the present invention;

FIG. 5 is a timing diagram at the time of feeding back forward channelquality information from an MS in accordance with another exemplaryembodiment of the present invention;

FIG. 6 is a block diagram illustrating a transmitter of an MS fortransmitting channel quality information in accordance with an exemplaryembodiment of the present invention;

FIG. 7 is a block diagram illustrating a BS for receiving channelquality information and performing scheduling and power control inaccordance with an exemplary embodiment of the present invention; and

FIG. 8 is a flowchart illustrating a control operation at the time ofallocating a packet data channel from a BS using channel qualityinformation in accordance with an exemplary embodiment of the presentinvention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofthe embodiments of the invention and are merely exemplary. Accordingly,those of ordinary skill in the art will recognize that various changesand modifications of the embodiments described herein can be madewithout departing from the scope and spirit of the invention. Also,descriptions of well-known functions and constructions are omitted forclarity and conciseness. Exemplary embodiments of the present inventionwill be described in detail herein below with reference to theaccompanying drawings. It is to be understood that the phraseology andterminology employed herein are for the purpose of description andshould not be regarded as limiting.

In a channel quality information feedback method proposed in anexemplary embodiment of the present invention, a mobile station (MS)feeds back two types of channel quality information. The two types ofchannel quality information proposed in the exemplary embodiments aresub-band-by-sub-band channel quality information and average channelquality information for a total band. In an exemplary scheduling methodof a base station (BS), the BS uses the sub-band-by-sub-band channelquality information for an Adaptive Modulation & Coding (AMC)transmission and allocates a diversity channel using the channel qualityinformation for the total band when a sub-band mapped to the channelquality information fed back from the MS cannot be allocated. Further,the BS uses the channel quality information for the total band tocontrol power of a control channel.

FIG. 4 is a timing diagram at the time of feeding back forward channelquality information from an MS in accordance with an exemplaryembodiment of the present invention. The feedback of forward channelquality information of the MS will be described with reference to FIG.4.

The MS transmits forward channel quality information in a block unit asillustrated in FIG. 4.

Blocks 401, 403, and 404 are mapped to intervals in whichsub-band-by-sub-band channel quality information is fed back from theMS. Each of the blocks 401, 403, and 404 transmit a pair of a sub-bandindex and channel quality information. Thus, each of the band-by-bandinformation transmission blocks 401, 403, and 404 indicate channelquality of a sub-band. When the band-by-band information transmissionblocks 401, 403, and 404 are transmitted in respective intervals orslots, a sub-band index can be omitted if sub-band information to be fedback is set, previously or otherwise, between the BS and the MS. In anexemplary embodiment, the number of sub-bands is set by negotiationbetween the BS and the MS when the MS feeds back the band-by-bandinformation transmission blocks 401, 403, and 404.

In FIG. 4, reference numerals 402 and 405 each denote an interval orslot for feeding back, from the MS, channel quality information for atotal band rather than a sub-band. That is, the total-band channelquality information transmission blocks 402 and 405 are included. Now,the total-band channel quality information transmission blocks 402 and405 will be described.

As described with reference to the prior art, a CQI stands for a“channel quality indicator” and indicates channel quality information.Thus, the channel quality information for the total band is averagechannel information for the total band. For example, when a system usesa band of 10 MHz, the MS measures an average signal-to-noise ratio (SNR)for the band of 10 MHz used in the system. An average value is taken byaccumulating measured values during a time period. The average value istransmitted through the total-band channel quality informationtransmission blocks 402 and 405. This average value for the total bandis not constantly used but is used only if needed. Thus, one of thetotal-band channel quality information transmission blocks 402 and 405can be conventionally transmitted in a unit of a time period 410. Thatis, the period 410 in which one of the total-band channel qualityinformation transmission blocks 402 and 405 are transmitted is a periodin which the average channel quality information for the total band istransmitted. The period 410 can be set by negotiation between the BS andthe MS. For example, if the period is 1, it means that an associated MSconstantly transmits the average channel quality information for thetotal band without feeding back the sub-band-by-sub-band channel qualityinformation. If the period is 2, it means that an associated MSalternately transmits the sub-band-by-sub-band channel qualityinformation and the average channel quality information for the totalband. FIG. 4 illustrates the case where the period is 3. In otherexemplary embodiments, the average channel quality information for thetotal band can be transmitted periodically or aperiodically.

FIG. 5 is a timing diagram at the time of feeding back forward channelquality information from an MS in accordance with another exemplaryembodiment of the present invention. An exemplary forward channelquality information feedback will be described with reference to FIG. 5.

In FIG. 5, blocks 501, 502, 503, 504, and 505 are mapped to intervals orslots in which the MS feeds back sub-band-by-sub-band channel qualityinformation. Blocks 511, 512, 513, 514, and 515 are mapped to intervalsor slots in which the MS feeds back channel quality information for atotal band. In the example of FIG. 5, different from FIG. 4, an averageCQI for the total band, sub-band indices mapped to a set number of bestCQIs, and their CQI values are transmitted whenever the channel qualityinformation is transmitted. When CQIs are not transmitted throughseveral best sub-bands at a particular point of time, a CQI for thetotal band is transmitted.

Because best CQIs are transmitted together with their sub-bandinformation in the example of FIG. 5, the BS can employ the remainingCQI values to compute an average value by excluding CQI values mapped tothe best sub-bands from CQI values mapped to all sub-bands. For example,it is assumed that the total number of sub-bands is 10 and the MStransmits CQIs of two best sub-bands. Then, the two sub-bands have avalue of more than the average value. Thus, a method can be employedwhich takes an average value of 8 sub-bands. That is, the BS excludesCQI values of the two sub-bands from CQI values of the 10 sub-bands, andtakes an average value of the remaining sub-bands from which the highestvalues have been excluded. When the sub-band of the best CQI requestedby the MS cannot be used in the above-described method, the average CQIvalue of the remaining sub-bands can be correctly detected by employingan average CQI value for the total band and an average CQI value of thebest sub-bands reported by the MS. Scheduling can be performed using acorrect CQI value of the remaining sub-bands. The above-describedprocess can be computed in the BS. Alternatively, the MS can beconfigured to report an average of the remaining sub-bands from whichthe best sub-bands corresponding to the individually reported sub-bandsare excluded. It is obvious that an average can be computed from whichsub-bands to be individually reported are excluded when the method isperformed in the MS.

There will be briefly described the reason why one MS feeds back twotypes of channel quality information, in other words,sub-band-by-sub-band channel quality information and average channelquality information for the total band, as in the exemplary embodimentsof FIGS. 4 and 5. When receiving the feedback of the two types ofchannel quality information, the BS uses the sub-band-by-sub-bandchannel quality information for an AMC transmission. If the BS cannotallocate a sub-band mapped to the fed-back channel quality informationto the MS, a diversity channel is allocated using other channel qualityinformation, in other words, average channel quality information for atotal band. Further, the BS uses the average channel quality informationfor the total band to control power of a control channel. This operationof the BS will be described in detail later with reference to FIG. 8.

It should be noted that an exemplary embodiment in which one MStransmits both the sub-band-by-sub-band channel quality information andthe average channel quality information for the total band is notlimited to FIG. 4 or 5, but can be variously modified.

FIG. 6 is a block diagram illustrating a transmitter of an MS fortransmitting channel quality information in accordance with an exemplaryembodiment of the present invention. The structure and operation of thetransmitter of the MS for transmitting the channel quality informationin accordance with an exemplary embodiment of the present invention willbe described with reference to FIG. 6.

A controller 601 measures sub-band-by-sub-band or orthogonalfrequency-by-orthogonal frequency channel quality information through aradio frequency (RF) unit or a demodulator and decoder (not illustratedin FIG. 6). The controller 601 generates channel quality informationfrom measured values input thereto as illustrated in FIG. 4 or 5. Thegenerated channel quality information is input to a channel encoder 602.The channel encoder 602 performs a channel encoding process for theinput channel quality information and inputs the channel-encoded channelquality information to a modulator 603. The modulator 603 modulates thechannel quality information in a set modulation scheme and then inputsthe modulated channel quality information to a physical channelconfiguration unit 604. The encoder 602 and modulator 603 may becontained in a modem (not shown). The physical channel configurationunit 604 inserts the channel quality information into a physical channelallocated in the reverse direction in an OFDMA system and then outputsthe physical channel to an RF transmitter 605. Then, the RF transmitter605 performs a band up-conversion process for the channel qualityinformation and then transmits the channel quality information in thereverse direction through an antenna ANT.

FIG. 7 is a block diagram illustrating a BS for receiving channelquality information and performing scheduling and power control inaccordance with an exemplary embodiment of the present invention. Theinternal structure and operation of the BS in accordance with anexemplary embodiment of the present invention will be described withreference to FIG. 7.

An RF receiver 701 of the BS of FIG. 7 receives a reverse signal throughan antenna ANT. The RF receiver 701 down-converts the received signaland then inputs the down-converted signal to a physical channelseparator 702. The physical channel separator 702 separates CQIinformation and then inputs the separated CQI information to ademodulator 703. Of course, the physical channel separator 702 extractsother control information and reverse data. Only contents relating tothe present invention will be described. The demodulator 703 demodulatesthe CQI information in a defined scheme and then inputs the demodulatedCQI information to a channel decoder 704. Then, the channel decoder 704extracts the CQI information as described with reference to FIG. 4 or 5through a channel decoding process. The extracted channel qualityinformation is input to a controller 710. The controller 710 includes achannel quality information controller 711, a scheduler 712, and a powercontroller 713. The channel quality information controller 711 receivesthe channel quality information and classifies band-by-band CQIinformation and total-band channel quality information. For example,when the channel quality information is received, average CQIinformation for the total band is kept during the period 410 asillustrated in FIG. 4 and is provided to the scheduler 712 or/and thepower controller 713. Further, when the channel quality information asillustrated in FIG. 5 is received, the average CQI information for thetotal band and the band-by-band channel quality information areclassified and are provided to the scheduler 712 or/and the powercontroller 713. As described above, when the average CQI for the totalband includes an individually reported average value and individuallyreported sub-band CQIs are excluded, the channel quality informationcontroller 711 computes an average value by excluding individuallyreported band values from the average CQI for the total band.Information computed by the channel quality information controller 711is provided to the scheduler 712 or/and the power controller 713. Thescheduler 712 performs scheduling using the CQI information input fromthe channel quality information controller 711 and other schedulinginformation. This scheduling process will be described in detail withreference to FIG. 8. The scheduler 712 performs the scheduling using theabove-described information and then provides a scheduling result to adata channel configuration unit 721 such that a data channel isconfigured. The scheduling result of the scheduler 712 is input to acontrol channel configuration unit 722 such that packet data controlinformation mapped to the scheduling result can be transmitted. Further,the scheduling result is input to the power controller 713.

Further, the power controller 713 receives CQI information scheduled bythe scheduler 712 and performs power control for the data channelconfiguration unit 721. At this time, the power controller 713 controlspower of a data transmission of the AMC mode using thesub-band-by-sub-band channel quality information when a data channeltransmission is an AMC transmission. On the other hand, when the datachannel transmission is the diversity transmission, the power controller713 performs power control using the average channel quality informationfor the total band among the channel quality information received fromthe channel quality information controller 711. At this time, theaverage channel quality information for the total band can use CQIs fromwhich a best CQI value is excluded as described above.

Further, the power controller 713 performs power control for the controlchannel configuration unit 722. In this case, when the control channeltransmission is the AMC transmission, power control for a controlchannel transmission of the AMC mode is performed using thesub-band-by-sub-band channel quality information. In contrast, when thecontrol channel transmission is the diversity transmission, the powercontroller 713 performs power control using the average channel qualityinformation for the total band among channel quality informationreceived from the channel quality information controller 711.

The data channel configuration unit 721 sets transmission power usinginformation of the power controller 713, generates data to betransmitted to each MS, and outputs the generated data to an RFtransmitter 723. Further, the control channel configuration unit 722configures a control signal to be transmitted to each MS or all MSs in acontrol channel, receives information of transmission power for a signalto be transmitted to each MS from the power controller 713, and outputsthe transmission power information to the RF transmitter 723. Theconfigured information is configured in a physical channel. The RFtransmitter 723 transmits the physical channel to each MS through theantenna ANT after a band up-conversion process.

FIG. 8 is a flowchart illustrating a control operation at the time ofallocating a packet data channel from the BS using channel qualityinformation in accordance with an exemplary embodiment of the presentinvention. The control operation of the BS will be described withreference to FIG. 8 when the packet data channel is allocated using thechannel quality information in accordance with an exemplary embodimentof the present invention. The case where channel quality information isfed back and used will be described.

The scheduler 712 of the BS collects available channel qualityinformation, in other words, sub-band-by-sub-band channel qualityinformation and average channel quality information for a total band instep 800. In this information collection, the channel qualityinformation controller 711 receives channel quality information fromeach MS and provides the received channel quality information to thescheduler 712. When collecting the channel quality information, thescheduler 712 collects information, for example, a state of a buffercontaining data to be transmitted to each MS and Quality of Service(QoS) information in step 802. Then, the scheduler 712 determineswhether the channel quality information received from a particular MSincludes the sub-band-by-sub-band channel quality information when achannel is allocated to the particular MS in step 804. If it isdetermined that the sub-band-by-sub-band channel quality information isincluded, the scheduler 712 proceeds to step 806. Otherwise, thescheduler 712 proceeds to step 810. First, the case where the scheduler712 proceeds to step 806 will be described.

When proceeding to step 806, the scheduler 712 determines whether asub-band mapped to the sub-band-by-sub-band channel quality informationcan be allocated to the MS. The scheduler 712 determines whether thesub-band requested by the MS has been already allocated to a differentuser with a priority. An order of forward data transmissions to all MSsis set according to a priority of each MS and a type of service in steps804 and 806.

If the associated sub-band can be allocated to the MS, in other words,the user, as the determination result of step 806, the scheduler 712proceeds to step 808. When proceeding to step 808, the scheduler 712decides to allocate the sub-band to the MS. That is, the scheduler 712decides to transmit data in the AMC transmission mode and sets a datatransmission rate of the AMC transmission mode using channel qualityinformation for the associated sub-band. However, if the associatedsub-band cannot be allocated to the user, in other words, the associatedsub-band has been already allocated to a different user, as thedetermination result of step 806, the scheduler 712 proceeds to step810. The process of step 810 will be described.

If the channel quality information received from the MS is not includedin the sub-band-by-sub-band channel quality information as thedetermination result of step 804, the scheduler 712 proceeds to step 810to decide to transmit data to the MS in the diversity transmission mode.Thus, the scheduler 712 sets a data transmission rate of the diversitytransmission using the average channel quality information for the totalband received from the MS in step 810.

The process of steps 804 and 806 is performed for each MS. If theprocess is completed, in other words, the decision in step 810 or 808 iscompleted for all MSs, the scheduler 712 proceeds to step 812. Whenproceeding to step 812, the scheduler 712 provides the power controller713 with sub-band information of the MS for transmitting data in the AMCmode and provides the power controller 713 with sub-band information ofthe MS for transmitting data in the diversity mode.

The power controller 713 generates a power control signal of a controlchannel using information received from the scheduler 712 and thechannel quality information controller 711 and then provides thegenerated power control signal to the control channel configuration unit722. Further, the power controller 713 generates a power control signalfor data to be transmitted in the AMC mode and then provides thegenerated power control signal to the data channel configuration unit721. That is, after configuring the data channel of the AMC transmissionmode or the data channel of the diversity transmission mode, the BSconfigures the control channel for transmitting control information forthe data channel and performs power control of the control channel usingthe average channel quality information for the total band received fromeach MS. The above-described process is performed in a unit of packetdata transmission.

As is apparent from the above description, exemplary embodiments of thepresent invention can minimize the forward performance degradation dueto a decrease in an amount of reverse channel quality informationthrough a scheduling method and a power control method. Further,exemplary embodiments of the present invention can effectively suppressan increase in the reverse load due to channel quality informationfeedback, and can increase the overall system capacity.

Although the exemplary embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions, and substitutions arepossible, without departing from the scope of the present invention.Therefore, the present invention is not limited to the above-describedembodiments, but is defined by the following claims, along with theirtotal scope of equivalents.

1. A method for feeding back channel quality information from a mobilestation in a wireless communication system based on Orthogonal FrequencyDivision Multiple Access (OFDMA), the method comprising: measuringsub-band-by-sub-band channel quality information; transmitting, in atleast one of a plurality of slots, channel-by-channel qualityinformation of a number of channels in order of sub-bands with betterchannel quality information; measuring average channel qualityinformation for a total band in the OFDMA wireless communication system;and transmitting, in at least one of the plurality of slots, the averagechannel quality information.
 2. The method of claim 1, wherein thechannel-by-channel quality information and the average channel qualityinformation are transmitted in every slot.
 3. The method of claim 2,wherein the measuring the average channel quality information comprisescomputing the average channel quality information by excluding atransmitted sub-band channel quality value.
 4. The method of claim 1,wherein the average channel quality information is transmitted in a timeperiod, and is transmitted using resources for transmitting thechannel-by-channel quality information.
 5. The method of claim 4,wherein the measuring the average channel quality information comprisescomputing the average channel quality information by excluding asub-band channel quality value transmitted in previous channel qualityinformation.
 6. A scheduling method for use in a base station of awireless communication system based on Orthogonal Frequency DivisionMultiple Access (OFDMA) for measuring and feeding back channel qualityinformation of sub-bands with better channel quality information andaverage channel quality information for a total band, the methodcomprising: determining whether an associated sub-band can be allocatedto an associated mobile station when channel quality information forsub-bands is included; setting a data transmission in adaptivemodulation and demodulation mode and setting a data transmission rateaccording to the channel quality information, when the associatedsub-band can be allocated; and setting a data transmission in diversitymode and setting a data transmission rate according to average channelquality information for a total band, when the associated sub-bandcannot be allocated.
 7. The method of claim 6, further comprisingsetting power of a control channel to be transmitted to each mobilestation using the average channel quality information for the totalband.
 8. The method of claim 7, wherein when channel quality informationof a sub-band for which the average channel quality information isreported is comprised, an average channel value for the total band isset again by excluding the channel quality information of the sub-band.9. The method of claim 6, wherein when a data transmission is set in theadaptive modulation and demodulation mode, power of data to betransmitted is set by sub-bands selected from among reported sub-bands.10. The method of claim 6, wherein a data transmission is set in thediversity mode, power of data to be transmitted is set by an averagechannel value for the total band.
 11. An apparatus for feeding backchannel quality information from a mobile station in a wirelesscommunication system based on Orthogonal Frequency Division MultipleAccess (OFDMA), comprising: a controller for measuringsub-band-by-sub-band channel quality information, generatingchannel-by-channel quality information of a number of channels in orderof sub-bands with better channel quality information, and measuring andgenerating average channel quality information for a total band in theOFDMA wireless communication system; a modem for encoding and modulatinginformation output from the controller; and a transmitter forconfiguring information output from the modem in a physical channel,performing a band up-conversion process for the physical channel, andtransmitting the physical channel.
 12. The apparatus of claim 11,wherein the controller alternately transmits the sub-band-by-sub-bandchannel quality information and the average channel quality informationfor the total band in a unit of a time period.
 13. The apparatus ofclaim 11, wherein the controller simultaneously transmits thesub-band-by-sub-band channel quality information and the average channelquality information for the total band.
 14. The apparatus of claim 11,wherein the controller sets channel quality by excluding channel qualityinformation of a reported sub-band when the average channel qualityinformation for the total band is set.
 15. An apparatus for receivingchannel quality information feedback and performing scheduling in a basestation of a wireless communication system based on Orthogonal FrequencyDivision Multiple Access (OFDMA), comprising: a channel qualityinformation receiver for receiving, demodulating, and decoding channelquality information received from a mobile station; a controller forextracting average channel quality information for a total band andsub-band index information mapped to best channel quality of aparticular mobile station on a basis of information from the channelquality information receiver, allocating a channel to each mobilestation in adaptive modulation and demodulation mode using sub-bandindices mapped to the best channel quality and a priority of each mobilestation after collecting scheduling information, and performingscheduling using average channel quality information of mobile stationsfor which allocation is impossible with respect to a sub-band of thebest channel quality or only the average channel quality information forthe total band; and a data channel configuration unit for configuringand transmitting a data channel on a basis of information controlled inthe controller.
 16. The apparatus of claim 15, wherein the controlleroutputs a data control channel power control signal for controllingpower of a control channel for providing control information of data tobe transmitted using the average channel quality information for thetotal band, and wherein the apparatus further comprises: a controlchannel configuration unit for setting power of the control informationof the data channel to be transmitted using the data control channelpower control signal and transmitting the control information.
 17. Theapparatus of claim 16, wherein the controller computes average channelquality by excluding power of a reported sub-band when the data controlchannel power control signal is generated if computation has beenperformed by including power of the sub-band for which the receivedaverage channel quality information for the total band has beenreported.
 18. A method for feeding back channel quality information froma mobile station in a wireless communication system based on OrthogonalFrequency Division Multiple Access (OFDMA) for configuring a sub-bandwith one or more orthogonal frequency resources, transmitting a pilotsignal using the orthogonal frequency resources in a time period,transmitting forward data using the orthogonal frequency resources, andreceiving channel quality information in a reverse direction, the methodcomprising: receiving the pilot signal; measuring channel qualityinformation of sub-bands and average channel quality for a total band;transmitting, in at least one of a plurality of slots,channel-by-channel quality information and indices of a number ofsub-bands in order of better channel quality information; andtransmitting, in at least one of the plurality of slots, the averagechannel quality information for the total band.
 19. The method of claim18, wherein the channel-by-channel quality information and the averagechannel quality information are transmitted in every slot.
 20. Themethod of claim 18, wherein the average channel quality information istransmitted in a time period, and is transmitted using resources fortransmitting the channel-by-channel quality information.